Homopolymer morphologies

Polyethylene s simplicity of structure has made it one of the most thoroughly studied polymeric materials. With an estimated demand of close to 109 billion pounds in 2000 of the homopolymer and various copolymers of polyethylene,24 it is by far the world s highest volume synthetic macromolecule. Therefore, it is still pertinent to study its structure-property relationships, thermal behavior, morphology, and effects of adding branches and functional groups to the polymer backbone. 

Random copolymers having an amorphous morphology generally exhibit a single having a value between the T s of the individual homopolymers. The exact value depends on the relative proportions of the respective monomers in the copolymer. 

An analysis of partition coefficient data and drug solubilities in PCL and silicone rubber has been used to show how the relative permeabilities in PCL vary with the lipophilicity of the drug (58,59). The permeabilities of copolymers of e-caprolactone and dl-lactic acid have also been measured and found to be relatively invariant for compositions up to 50% lactic acid (67). The permeability then decreases rapidly to that of the homopolymer of dl-lactic acid, which is 10 times smaller than the value of PCL. These results have been discussed in terms of the polymer morphologies. 

The synthesis of organotin oligosteracrylate i.e. dimethylstannyl dimethacrylate, and the production of the cross-linked homopolymers on its basis have been reported. Morphology, mechanical and relaxation properties of poly(dimethyl-stannyl dimethacrylate) have been investigated 67). 

The emphasis is on commercial materials and formulations. The reason is that commercial materials are rarely pure materials. A pure homopolymer is a rare species in the real-world materials. To arrive at the desired material s properties, either a copolymer is used, sometimes a blend or a dispersion, or additives or filler materials including rubber particles, carbon black or fibres of various type and make may be added, and are thus commonplace in commercial products. This implies a more complex constitution and morphology than expected for pure polymers. However, obviously, the methods described herein can be applied to pure, unmodified, polymers as well. 

In what follows, we use simple mean-field theories to predict polymer phase diagrams and then use numerical simulations to study the kinetics of polymer crystallization behaviors and the morphologies of the resulting polymer crystals. More specifically, in the molecular driving forces for the crystallization of statistical copolymers, the distinction of comonomer sequences from monomer sequences can be represented by the absence (presence) of parallel attractions. We also devote considerable attention to the study of the free-energy landscape of single-chain homopolymer crystallites. For readers interested in the computational techniques that we used, we provide a detailed description in the Appendix. ... 

Noguchi, H. Yoshikawa, K., Morphological variation in a collapsed single homopolymer chain, J. Chem. Phys. 1998,109, 5070-5077... 

Morphology. Observations with the light microscope, under polarized light, showed that the end blocks in the case of both types of polymers crystallized in the form of the usual spheru-lites, but not as well as the analogous homopolymer, H2-l,4-polybutadiene. The formation of the spherulites was improved with increasing end-block content and/or higher molecular weight of the end blocks. 

JThe effect of the substituent on the properties of the polyphosphazenes is not fully understood. For instance, [NP(OCH ) ]n and [NP C CH. homopolymers are elastomers (8,29). Synthesis using lithium, in contrast to sodium, salts is claimed to produce rubber-like fluoroalkoxyphosphazene polymers (30). The presence of unreacted chlorine or low molecular weight oligomers can affect the bulk properties (31,32). Studies with phosphazene copolymers both in solution and in the bulk state (29,33-38) indicate a rather complex structure, which points out the need for additional work on the chain structure and morphology of these polymers. 

In analogy to linear-block copolymers different cases can be distinguished when blending asymmetric miktoarm (PS-PI)n-PS and H-shaped (PS-PI)3-PS-(PI-PS)3 copolymers with homopolymer PS [122]. If the latter s molecular weight is lower than the respective PS block, a transition from the L structure to hexagonally packed cylinders without observation of an intervening cubic morphology is observed in the case of the (PS-PI)n-PS types. If the H-shaped (PS-PI)3-PS-(PI-PS)3 star-block copolymer is blended with 30% to... 

The TEM (Fig. 44) and SAXS data clearly indicate that the structure is lamellar to the first order but modified by channels in the PI layers, leading to a PL pattern. However, Fredrickson s theoretical results indicate that in the SSL this structure is not the most favourable one [123]. In the WSL, similar PLs are to occur for equal weight fractions, even though lamellae are expected in that region [124]. A similar behaviour has been observed in the case of PI2PS homopolymer blends for the PL morphology [15]. 

The effect of blending an AB diblock copolymer with an A-type homopolymer has been the subject of many research activities. On a theoretical basis the subject was investigated e.g. by Whitmore and Noolandi [172] and Mat-sen [173]. If a diblock exhibiting lamellae morphology is blended with a homopolymer of high molecular weight, macrophase separation between the... 

The appearance and persistence of core-shell structures as well as the occurrence of phase separation are attributed to a small asymmetry in the X -parameters (xPS-pi = 0.06, xpi-pdms = 0.09 and xps-pdms = 0.20). Hence, a PDMS core surrounded by a PI shell embedded in a PS matrix results in a smaller inner diameter interfacial area, relative to that for the PS-PI case. In a blend of a PS-fo-PI-fc-PDMS triblock with PS and PDMS homopolymers, more PS homopolymer is expected to be found in the corona of the PS block than PDMS homopolymer in the corona of the PDMS block because the penalty for contact between the PI block and PDMS homopolymer is larger. In consequence, the distribution of homopolymers favours an expanded PS-PI interface, making the core-shell morphologies, gyroid and cylinder, more prevalent. 

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